Driving arrangement for passive time indication devices

ABSTRACT

A driving arrangement for passive time indication devices wherein a passive indication device is connected between the output terminal of a double throw-type switching element and a terminal having a first potential such that the difference between said first potential and a second potential applied to the output terminal of said switching element when said switching element is in a first position is sufficient to excite the passive time indication device while the difference between said first potential and a third potential applied to said switching element output terminal when said switching element is in a second position is less than the threshold voltage of the passive time indication element.

United Sta Hama et a1.

[ Mar. 19, 1974 DRIVING ARRANGEMENT FOR PASSIVE TIME INDICATION DEVICES 1 Primary Examiner-Richard B. Wilkinson Assistant Examiner-Edith Simmons Jackmon [75] Inventors: Tetsuro I-Iama; Izuhiko Nishimura, Attorney Agent or Firm Blum, Moscovitz, Friedman both of Suwa, Japan & K

aplan [73] Assignee: Kabushiki Kaisha Suwa Siekosha,

Tokyo, Japan [57] ABSTRACT [22] Filed: 28, 1972 A driving arrangement for passive time indication devices wherein a passive indication device is connected PP N0.: 232,461 between the output terminal of a double throw-type [30 Foreign Application p l a' switching element and a terminal having a first poten- F b 27 1971 J 469804 tial such that the difference between said first potene apan tial and a second potentlal applied to the output termi- [52] US. Cl 58/50 R, 350/160 LC nal of said Switching element when said switching [51 Iltt. C1. G041) 19/30 ment is in a first position is Sufficient to excite the Fleld of 'u'ryn; 7:: 53 R1 2115) 07R sive time indication device while the difference be 340/3091 152 3363 tween said-first potential and a third potential applied 350/160 LC; 307/38 to said switching element output terminal when said switching element is in a second position is less than [56] Cited the threshold voltage of the passive time indication el- UN1TED STATES PATENTS ement.

3,664,] 18 5/1972 Walton 58/23 A X 5 Claims, 7 Drawing Figures 3.575,492 4/1972 Nester et a1. 350/160 LC 3.576.099 4/1971 Walton 58/50 R 3.505.804 4/1970 Hofstein 58/50 R ZEflKGE' 655/570,? 9 c9 /3 7 Eels/5701c /4 on. In: as/50 DRIVING ARRANGEMENT FOR PASSIVE TIME INDICATION DEVICES BACKGROUND OF THE INVENTION This invention relates to a driving arrangement for passive time indication devices adapted for actuation by an electric signal to provide a visual time indication in electric timepieces. In recent years, passive time indication elements such as liquid crystal display devices have been produced which change the condition of scattering, absorption, transmission or polarization of light in response to an electric signal in order to provide a visual display. Such passive time indication devices generally require small amounts of power for operation and are particularly suitable for application to fully electronic watches, and in particular, to small-sized fully electronic wrist watches. On the other hand, such passive indication devices generally require a high voltage for operation, resulting in the problem that a slight leakage current in the driving circuit reduces the efficiency of the indicating function. By taking into consideration the voltage characteristics of such passive time indication elements, the foregoing deficiencies have been eliminated.

SUMMARY OF THE INVENTION Generally speaking, in accordance with the invention, a driving arrangement for passive time indication devices is provided wherein a passive time indication device is connected between the output terminal of a double throw-type switching element and a terminal having a first potential applied thereto. Said switching element may consist of a pair of separate switches connected to a common output terminal, mechanical switching devices, and solid state switching devices. Second and third potentials are respectively applied to the two inputs of said switching element for respective application to said output terminal when said switching element is in one of first and second switching modes. The value of said first potential is such that the difference between said first and second potentials is sufficient for exciting said passive time indication element while the difference between said first and third potentials is less than the threshold voltage of said passive indication element. Accordingly, it is an object of this invention toprovide a driving arrangement suitable for driving passive time indication elements to provide time indication for watches.

Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification and drawings.

The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying drawings, in which:

FIG. 1 is a graphical representation of the typical voltage-brightness characteristics of a passive indication element;

FIG. 2 is a block diagram of a general driving circuit for such passive indication element;

FIG. 3 is a block diagram illustrating the driving arrangement in accordance with the invention for such passive indication elements;

FIG. 4 is a circuit diagram of a second embodiment of the double throw-type switching element in accordance with the invention;

FIG. 5 is a circuit diagram of one embodiment of the driving arrangement in accordance with the invention;

FIG. 6 is a block diagram of an electronic watch incorporating the driving mechanism in accordance with the invention; and

FIG. 7 is a circuit diagram of a circuit for producing the three potentials required in connection with the driving arrangement in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, a graphical representation of the voltage-brightness characteristics generally found in passive time indication elements is depicted. In said graphical representation, the axis of abscissa x represents the voltage applied to the passive time indication element with the origin being taken at O. The axis of ordinates y represents the brightness of said passive time indication element relative to a maximum effective value for indication assigned the value of one. Curve 1 is a voltage-brightness curve in which the brightness is low between the origin 6 and a voltage V,, while between said voltage V; and a voltage V there occurs a change from the low brightness state (not excited state) to the high brightness state (excited state). In addition, curve 1' shows the relation between voltage and the brightness in the reverse situation to that of curve 1. The voltage V, is referred to as the threshold voltage in this application.

As shown in FIG. 2, when a series circuit consisting of a passive indication element 4 and a switching element 5 is inserted between voltage sources 2 and 3, and when a leakage resistance 6 present during the opened state of switching element 5 is small, the divided voltage applied to the passive indication element 4 may exceed the threshold voltage V so that said passive indication element approaches the excited state. The addition of a shunt resistance parallel to the passive indication element to compensate for the above-mentioned undesirable result is likewise undesirable, since the value of the resistance needed must be smaller than the leakage resistance 6, thereby increasing the portion of the current which is unavailable for display purposes.

The arrangement in accordance with the invention as illustrated in FIG. 3, wherein a first voltage source is connected between terminals 7 and 8 and a second voltage source is connected between terminals 7 and 9, said second voltage source being of a value not less than said first voltage source. The input terminal of a double throw-tupe switching element 11 is also connected between terminals 7 and 8, said switching element having a common output terminal 12 for selective connection to either of terminals 7 and 8. A passive indication element 10 is connected between terminals 9 and 12 while leakage resistors 13 and-l4 are connected between the respective input terminals 7 and 8 of double throw-type switching element 11 and passive indication element 10 (terminal 12).

As more particularly shown in FIG. 4, while a unitary double-throw switching element as depicted in FIG. 3

may be used, said double-throw-type switching element may also take the form of two single-throw-switching elements 15 and 16 which operate oppositely, or by any element having a similar function.

In the switching mode where terminal 12 is connected to terminal 7 through the double-throw type switching element, passive indication element 10 is connected between terminals 7 and 9, so that the voltage of the second voltage source is applied thereto. On the other hand, in the switching mode wherein terminal 12 is connected to terminal 8 through said doublethrow-type switching element, passive indication element 10 is connected between terminals 8 and 9, so that the difference in voltage between said first and second voltage sources are applied thereto. By insuring that the second voltage source is of a value great enough to excite passive indication element 10, and by insuring that the voltage of the first voltage source is of a value less than the value of said voltage of said second voltage source by an amount within the range wherein said passive indication element will not be excited (i.e., a value less than the threshold voltage), the excitation condition of the passive indication element can be regulated by setting the switching mode of double-throwtype switching element 11 between two values.

By selecting the first voltage source so that it has a value less than the second voltage source, it is possible to use semiconductor switching elements having nonlinear leakage resistance in response to voltage as the double-throw-type switching element. An example of such an arrangement is depicted in FIG. 5, wherein the double-throw-type switching element consists of an enhancement type P-channel insulated gate field effect transistor 23 and an enhancement type N-channel insulated gate field effect transistor 24. The passive indication element 22 is in the form of a nematic liquid crystal. Taking the potential at a terminal 17 connected to the source of transistor 24, a first positive potential is applied to terminal 18 connected to the source of transistor 23 and a second positive potential sufficient to excite indication element 22 and of a value not less than the value of said first positive potential is connected to terminal 19, which in turn is connected to one side of passive indicator element 22, the other side of said passive indicator element being connected to common output terminal 21 connected between the respective drains of transistors 23 and 24. The difference between the second positive potential and the first positive potential is selected to be smaller than the threshold voltage of passive indication element 22.

The control of the double throw-type switching element of FIG. is achieved through terminal 20 connected to the respective gates of transistors 23 and 24. Thus. said transistors are placed in a first switching mode when a potential nearly equal to the potential of terminal 17 (approximately zero potential) is applied to terminal 20. In this mode, gate G of transistor 24 is placed at nearly zero potential so that the resistance between the source SN and the drain D thereof is placed at an extremely large value. On the other hand, the gate G of transistor 23 is given a potential of one direction so that the resistance between source Sp and drain D decreases substantially. As a consequence, the potential at the common connecting electrode 21 between the respective drains of transistors 23 and 24 becomes equal to the first positive potential applied to terminal 18 and a voltage nearly equal to the difference between the second and first positive potential is applied to passive indication element 22. Since this difference potential is lower than the threshold voltage of said passive indication element, said element is not excited. At this time, if the current flowing from terminal 19 to terminal 21 exceeds the current flowing from drain D of transistor 24 to terminal 17, drain D, of transistor 23 assumes a positive potential relative to terminal 18. However, since a diode has been formed in one direction between drain D of transistor 23 and the substrate Su thereof, the potential in question becomes almost equal to the potential of terminal 18.

In the second switching mode, wherein a positive potential nearly equal to the potential of terminal 18 is applied to terminal 20, gate G of transistor 23 is placed at nearly zero potential so that the resistance between source Sp and drain Dp thereof are brough to an extremely large value. On the other hand, the gate 6,, of transistor 24 has a potential of one direction applied thereto so that the resistance between source S and drain D thereof is reduced considerably. For this reason, the potential at common connecting terminal 21 is substantially at the standard potential (zero potential) and a potential nearly equal to the second positive potential is ap plied to passive indication element 22 to excite said element.

While in the foregoing embodiment, a pair of transistors was incorporated as the double throw-type switching element, other suitable double throw-type switching elements may be substituted therefor consisting either of unitary switching elements or combinations of switching elements, provided the functions of the double throw-type switching elements of FIGS. 3 and 4 are performed.

Referring now to FIG. 6, a block diagram of a watch incorporating the driving arrangement in accordance with the invention is depicted. In said embodiment, the double throw-type switching element 55 may take the form of a complimentary insulated gate field effect transistor arrangement such as is depicted in FIG. 5. Further, the passive indication elements are of the nematic liquid crystal type, the indication elements providing a digital display of hours and minutes through the use of a seven bar display capable of displaying any number from one to nine at each digit of said hour and minute indication. For this purpose, each digit would be represented by a liquid crystal display device of the passive indication type having a common electrode, a segmented electrode formed from said seven bars and liquid crystal material of the nematic type therebetween. Indication of seconds is formed by means of a round liquid crystal display having six pie-shaped sectors which are sequentially flickered in response to a signal having a period of one second, each of the pieshaped sectors being flickered for a period of 10 seconds.

In the electronic watch of FIG. 6, a high frequency time standard signal is generated in an oscillator 25 and divided into a signal having a 1 second period by a frequency divider 26. The 1 second signal from divider 26 is applied to a l/lO divider 27 which serves to count the 1 second signals to produce a I0 second signal for application to H6 divider 28. Divider 28 counts the 10 second signals to produce a 1 minute signal for application to the next stage.

The state output of l/6 counter 28 is applied to a decoder 32 adapted to produce six output signals, one of said output signals being associated with each of the sectors of the second indicator. Said output signals are applied to gate circuits 36 which consist of six AND gates 54, one of which is associated with each second indicator sector, for receiving the associated output signal from decoder 32 and a 1 second signal from terminal 56 connected to the output of divider 26. The output of each AND gate 54 is connected to the control of a double throw-type switching element 55, in this case to the respective gates of the insulated gate type field effect transistors, to control the switching mode of said switching element. The input terminals of each switching element 55 in driving circuit 37 are respectively connected to ground potential V and to potential V The output terminal of each of said switching elements is connected to one of the sector electrodes 45 of the second indicator, the common electrode 47 thereof being connected to voltage V In this manner, each sector is sequentially flickered at a frequency of 1 Hz for a period of seconds.

A 1/ l0 divider 29 receives the 1 minute signal from divider 28 through OR gate 46, and produces a 10 second signal output. The state output of divider 29 is applied to a decoder 33 for producing seven outputs corresponding to the seven bars on the minute digit display segmented electrode 44. Each output of decoder 33 is applied to a double throw-type switching element 55 in driving circuit 38 which functions in a manner similar to the double-throw-type switching element 55 of driving circuit 37. In a similar manner, divider receives the 10 minute signal from divider 29 through OR gate 48 to produce a 1 hour signal. The state signals of divider 30 are applied to decoder 34 to driving circuit 39 which provides the driving voltages for the seven bar display of the 10 second digit represented by segmented electrode 43.

Finally, the 1 hour signal output of 1/6 divider 30 is applied to a l/l2 divider 31, the state of which drives the 10 hour digit segmented electrode 42 through decoder and driving circuit in the same manner as the other digits of the display. A switch 52 resets the states of the respective frequency dividers and counters to their initial states through a connection to terminals 53 thereof, while switches 49, 50 and 51 set the respective digits of the 1 minute display the 10 minute display and the 1 hour display to the desired figures by connection to the respective OR gates 48. Each time one of switches 49, 50 and 51 is in its respective ON state, a digit is added logically to the divider associated therewith so as to add one count to each divider to advance the state of that divider by one digit.

In the embodiment of FIG. 6, the potentials of the re- V(: VE VL- When the nematic phase liquid crystal it driven, it is necessary that, taking the threshold voltage as V and the voltage sufficient for indication as V that said potential should conform to the following relations:

VC VON,

and

Since,

V V V it is possible in the arrangement in accordance with the invention to supply a voltage higher than the voltage applied to the driving circuit to the indication element as mentioned above, so that substantial advantages such as clear visibility of indication, simplification of design of driving circuit and reduction of electric power consumption can be achieved.

Referring now to FIG. 7, one example of a voltage boosting circuit for obtaining potentials V V and V from a single battery is depicted. In such circuit, a toroidal core which provides maximum boosting efficiency while minimizing size is wound with a driving coil 63 and a detecting coil 64. Driving coil 63 is connected across the series connection of a battery 61 and the emitter-collector path of a transistor 62. Driving coil 64 is connected between a resistor 65 and the base of said transistor. An oscillator AC voltage is delivered to the secondary coil 66 and is rectified by diodes 67 and smoothing condensers 68 to produce the desired potentials V V,; and V which satisfy the conditions required in accordance with the invention. 7

It will thus be seen that the objects set forth above, and those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above construction without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

What is claimed is:

1. An electronic timepiece comprising oscillator means for producing a high frequency time standard signal; divider circuit means for producing low frequency timing signals in response to said high frequency time standard signal; decoder means for pro-' ducing display actuation signals in response to said timing signals; passive indication elements actuable in response to said display actuation signals to provide a visual indication of time; double-throw-type switching means having first and second input terminals and an output terminal for selective placement in either of a first switching mode at which said first input and said output terminals are coupled and a second switching mode at which said second input and said output terminals are coupled; terminal means, said passive indication means being connected between said switching means output terminal and said terminal means; and means for applying a first potential to said terminal means, and second and third potentials to said first and second switching means input terminals, respectively, said potentials being selected to have a value such that the difference between said first and second potentials is sufficient to actuate said passive indication means to provide a visual indication, and the difference between said first and third potentials is less than the threshold voltage of said passive indication means at which such visual indication is first produced, said double-throwtype switching means being coupled to said decoder means for selective disposition in one of said first and second switching states in response to said display actuation signals.

2. A driving arrangement as recited in claim 8, wherein said double-throw-type switching means includes a pair of coordinately actuated single-throwtype switching means, one of said single-throw-type switching means being connected between each of said inputs and said output.

3. A driving arrangement as recited in claim 8, wherein said double-throw-type switching means comprises an N-channel and a P-channel field effect transistor connected with their respective source-drain paths in series, the respective gates being connected together for coordinate actuation, said output being at the intersection of the respective source-drain paths, said inputs being on the side of said source-drain paths opposite from said output.

4. A driving arrangement as recited in claim 1, wherein said passive indication means is a liquid crystal display.

5. A driving arrangement as recited in claim 1, wherein said means for applying said first, second and third potentials includes a battery, transformer means having primary and secondary windings; further oscillator means including said battery and primary windings for applying an AC low voltage to said transformer means primary winding, said secondary winding including a pair of end terminals and a center tap, rectifier means connected to said secondary winding end terminals and center tap for producing said first, second and third potentials at the three outputs thereof.

STATES PATENT OFFICE CERTIFICATE OF coR-EUHN Patent NO. 3,797,225 Dated Marc 2h 19,, 1974- Iflventoflsj TetsuIro Hama and Izuhiko Nishimura It is certified that error appears in the above-identified patent and that said Letters' Patent are hereby corrected as shown below:

Column 7, lit 1e ll, inclaim 2, cancel "8" and substitute 1-.

Column 7, in claim-1.3 C l H nd substitute --1-.-, t I

Signed and sealed this 24th day Of December 1974.

(SEAL) Attest:

I I-1cCOY M. clssom JR. c .v MARSHALL DANN Attesting Officer Commissioner of Patents F ORM PO-105O (10-69) USCOMM-DC GOING-P69 lLS GOVERNMENT PRINTING OFFICE I969 0-366-334. 

1. An electronic timepiece comprising oscillator means for producing a high frequency time standard signal; divider circuit means for producing low frequency timing signals in response to said high frequency time standard signal; decoder means for producing display actuation signals in response to said timing signals; passive indication elements actuable in response to said display actuation signals to provide a visual indication of time; double-throw-type switching means having first and second input terminals and an output terminal for selective placement in either of a first switching mode at which said first input and said output terminals are coupled and a second switching mode at which said second input and said output terminals are coupled; terminal means, said passive indication means being connected between said switching means output terminal and said terminal means; and means for applying a first potential to said terminal means, and second and third potentials to said first and second switching means input terminals, respectively, said potentials being selected to have a value such that the difference between said first and second potentials is sufficient to actuate said passive indication means to provide a visual indication, and the difference between said first and third potentials is less than the threshold voltage of said passive indication means at which such visual indication is first produced, said double-throw-type switching means being coupled to said decoder means for selective disposition in one of said first and second switching states in response to said display actuation signals.
 2. A driving arrangement as recited in claim 8, wherein said double-throw-type switching means includes a pair of coordinately actuated single-throw-type switching means, one of said single-throw-type switching means being connected between each of said inputs and said output.
 3. A driving arrangement as recited in claim 8, wherein said double-throw-type switching means comprises an N-channel and a P-channel field effect transistor connected with their respective source-drain paths in series, the respective gates being connected together for coordinate actuation, said output being at the intersection of the respective source-drain paths, said inputs being on the side of said source-drain paths opposite from said output.
 4. A driving arrangement as recited in claim 1, wherein said passive indication means is a liquid crystal display.
 5. A driving arrangement as recited in claim 1, wherein said means for applying said first, second and third potentials includes a battery, transformer means having primary and secondary windings; further oscillator means including said battery and primary windings for applying an AC low voltage to said transformer means primary winding, said secondary winding including a pair of end terminals and a center tap, rectifier means connected to said secondary winding end terminals and center tap for producing said first, second and third potentials at the three outputs thereof. 